Site-exposed Ti3C2 MXene anchored in N-defect g-C3N4 heterostructure nanosheets for efficient photocatalytic N2 fixation

Exploring highly active centers for N ;N triple-bond activation and the suppression of the competing H-2 evolution reaction (HER) are key considerations for photocatalytic N-2 fixation. As a novel 2D transition-metal carbide, Ti3C2 nanosheets (MXenes) have been recently considered as a promising N-2 reduction reaction (NRR) active center. However, little of the expected progress in the use of Ti3C2 for photocatalytic N-2 fixation has been achieved. Herein, we report a novel 2D/2D Ti3C2/N-defect g-C3N4 heterostructure photocatalyst exhibiting highly enhanced photocatalytic nitrogen fixation activity, with an NH3 yield of 5.792 mg h(-1) g(-1). This study demonstrates that the heterostructure was constructed by filling the oxygen-terminals of Ti3C2 in the N-defects of g-C3N4 to form C-O-Ti interactions. Together, the construction of the hetero-interface and the introduction of N-defects contribute to rapid interfacial charge transfer to the active sites. Importantly, the exposed edge Ti of Ti3C2 was confirmed to be the active site for N-2 adsorption and activation, and these active Ti sites exhibit desirable NRR selectivity via suppressing the competing HER. Finally, a mechanism for photocatalytic N-2 fixation was proposed to reveal the evolution of the redox circle that originated from the multi-valence Ti species during the N-2 adsorption, activation, and dissociation process.